Assessment of Biodiversity at the Local Scale for Environmental Impact Assessment and Land-use Planning

Figures & data

Table 1. TAG ecological evaluation

Criterion	Value	Examples
High importance and rarity on an international scale with limited potential for substitution	Very high	Internationally designated sites
High importance and rarity on a national or regional scale with limited potential for substitution	High	Nationally designated sites
	Regionally important sites with limited potential for substitution
High or medium importance and rarity at a local or regional scale with limited potential for substitution	Medium	Regionally important sites with potential for substitution.
	Locally designated sites
Low or medium importance and rarity on a local scale	Low	Undesignated sites of some local biodiversity and earth-heritage interest
Very low importance and rarity on a local scale	Negligible	Other sites with little or no local biodiversity and earth heritage interest

Table 2. The ‘Ratcliffe criteria’

Ratcliffe criterion	Qualification	Examples of national and international measures
Primary criteria
Size	Of a size appropriate to maintain its function; for example, sites for top predators may need to be extensive, species rich grasslands can be limited in area but stable, populations should be at above threshold levels for viability and resilience	Some sites assessed in terms of the size of population supported; for example, numbers of over-wintering wildfowl or waders, breeding seabird colonies, bat roosts
		The 1% level of national and global bird populations is used respectively for the notification of SSSI (UK) and globally important bird areas (IBA) or key biodiversity areas (KBA)
Diversity	Number of species present (generally the species richness of a defined group) in a site. Comparisons of diversity should apply to sites of the same community type	The UK NVC provides descriptions of characteristic plant communities used as a baseline for comparison
		Corine biotopes describe vegetation communities in Europe
		Diversity indices (e.g. Simpson, Shannon) can provide comparative assessments between sites
Naturalness	Habitats largely unmodified by human activity (e.g. salt marsh, blanket bog). Some anthropogenic habitats retaining characteristics of low disturbance may be included (e.g. heathlands, meadows)	NVC communities, Corine biotopes, indicator species, presence and proportion of native and non-native species, professional judgement, recorded history of the site
Rarity	Applied to habitats or species where areas are limited, population numbers low or the habitat or species limited in distribution	NVC and Corine biotopes can define rare habitat types
		Habitats <10,000 hectares in the UK considered rare
		UK species occurring in <15, 10 × 10 km squares of the national grid are considered nationally rare (i.e. <0.5% of the total); from 16–99, 10 km squares (nationally scarce (<3.5% of the national total 10 km squares)
		Red Data Book species. International Union for Conservation of Nature (IUCN) Red List
		Endemics may be rare at particular scales
Fragility	Habitats or species vulnerable to disturbance and loss because of small area, low population or reliance on a single key resource	Mainly professional judgement backed up by research data or precedent. Red Data or IUCN Red listing may imply fragility or vulnerability. Trend analysis for species or species assemblages
		Small local populations may have particular importance to meta- populations in maintaining gene flow
		Certain endemics may be vulnerable to the effects of competition from alien species
Typicalness	Reflects the need to include the more abundant habitats communities and species, those at the centre of their natural range	NVC or Corine biotope analysis for plant communities, community and species distribution data, professional judgement
Secondary criteria
Recorded history	Sites with a good record of study may contribute to scientific knowledge and cultural awareness
Potential value	Degraded sites with remnants of the original ecological formation that may be readily restored	Professional judgement, although NVC community analysis may assist in identifying sites
		Habitat modelling; for example, physical habitat simulation (PHABSIM) for river systems, Predictive System for Multimetrics (PSYM) for ponds
Position in an ecological unit	Notes the value of contiguity of different habitats (the antithesis of fragmentation) or the particular ecological qualities of seral stages or ecotones. Can include wildlife corridors or networks	Vegetation community analysis (e.g. NVC, Corine) may assist in the identification of related communities according to physical gradients, ordination analyses
Intrinsic appeal	Habitats, and habitats supporting species, with particular public appeal. Can include areas scheduled for wildlife and public amenity, green corridors.	Professional judgement and/or results of stakeholder surveys and consultation. Certain ‘flagship’ species with intrinsic appeal may also act as ‘umbrella’ or ‘keystone’ species where their protection requires conservation of specific habitats or key ecological communities

Table 3. Examples of criteria for selection of non-statutory wildlife sites

Primary criterion	Examples of qualifying criteria
Size	Woodland habitats >1 hectare, heaths >0.5 hectares (Dorset Wildlife Trust, 2001)
	The regular occurrence of 1% or more of the county population (e.g. of bird species)
	With 0.5% or more of the National population of bird species. (Derbyshire Biodiversity, undated; Hertfordshire Habitat Survey, undated)
Diversity	Defined NVC communities (Cambridgeshire County, 2006; Gwent Wildlife Trust, 2004; Hertfordshire Habitat Survey, undated) deemed to be important at a county level or within the Natural Area (Derbyshire Biodiversity, undated)
	Semi natural plant communities as defined by listed indicator species; for example, for ancient woodlands, grasslands, ponds (Gwent Wildlife Trust, 2004; Nottinghamshire Biological Record Centre, undated; Derbyshire Biodiversity, undated; Essex Wildlife Trust, 2007)
	Use of the Hedgerow Regulations 1997 to provide criteria for notable hedgerows.
	Habitat structure; for example, rivers (Derbyshire Biodiversity, undated; Cambridgeshire County, 2006)
	Breeding bird assemblages using threshold index scores derived from the NCC 1989 guidelines (Cambridgeshire County, 2006; Dorset Wildlife Trust, 2001; Hertfordshire Habitat Survey, undated). (The NCC bird indices are scored in accordance with abundance in the UK, i.e. rarer species gain a higher index value.) Localities with over 50 breeding species, 60 wintering species or 100 passage species (Cambridgeshire County, 2006)
	Amphibian assemblages >3 native species. (Cambridgeshire County, 2006; Essex Wildlife Trust, 2007)
	Reptile assemblages >3 native species. (Cambridgeshire County, 2006; Essex Wildlife Trust, 2007).
	Insect rich habitats supporting >4 bat species (Hertfordshire Habitat Survey, undated)
	River habitat assessment scores under RIVPAC and Pond habitat assessment scores under PSYM (see http://www.brookes.ac.uk/pondaction/PSYM2.htm!) (Dorset Wildlife Trust, 2001)
	Community Conservation Index (CCI) for freshwater invertebrate communities (Chadd and Extence, 2004) and other indices for ecosystem water quality (British Standards Institute, 2000a&b).
	Invertebrate indices (JNCC Invertebrate Site Register, now on the National Biodiversity Network) (Derbyshire Biodiversity, undated)
Naturalness	Ancient Woodlands (Ancient Woodland Inventories, now available on http://www.magic.gov.uk/)
	Defined NVC communities
	Presence of normally between 5 and 10 plant species, depending on habitat, from a list of indicator plant species to define habitats; for example, woodlands, grasslands, ponds, of county value (Derbyshire Biodiversity, undated; Cambridgeshire County, 2006)
	Index thresholds for indicator plant species present where Local Red Data species may be indexed at double the value (Derbyshire Biodiversity, undated)
	Habitat structure; for example, rivers (Derbyshire Biodiversity, undated; Cambridgeshire County, 2006)
Rarity	County rarity being a species occurring in <1% of tetrads, Scare species <4% of tetrads (Hampshire)
	Presence of rare breeding birds being those with less than 300 pairs nationally (Hertfordshire Habitat Survey, undated) or fewer than 20 pairs at a county level (Derbyshire). Species rarity indices based on presence in percentage proportion of county tetrads; for example, for birds (Hertfordshire Habitat Survey, undated)
	IUCN Red Data Book species (most counties)
	Red Data and Nationally Scarce insects (occurring in <100, 10 km^2) to provide a Species Quality Index (Essex Wildlife Trust, 2007)
	Selected Red listed (JNCC/British Trust for Ornithology, 2002) birds (Hertfordshire Habitat Survey, undated; Derbyshire Biodiversity, undated)

Box 1. Riverside Infrastructure Development

Development proposals were made affecting a small section of river and river bank in the tidal reach of one of south-west England's ria rivers. Of the ecological receptors considered, two groups came under particular focus in the assessment of local biodiversity, bats and wading birds.

The ecological appraisal indicated that a small number of horseshoe bats (Annex II EC Directive) frequented this section of river and its riverside buildings but at numbers below the level of county importance. However, previous radio-tracking studies indicated that this section of river offered only one of two crossing points for bats commuting from a major roost, notified as a European Directive SAC. This key attribute of the site in a regional network for bats was considered to increase the value of the site to that of county importance (Garland & Markham 2008 consider the legal background to the protection of such commuting corridors).

Similarly, a small population of wading birds were under potential impact from the development, using this section of the river shore mainly as a high-tide roost. Numbers of wintering redshank varied between 20 and 30 birds. This small population approximates to 1% of the county population. Redshank is included in the British Red data bird list in view of the importance of the UK for the migratory and over-wintering population. A second factor of relevance was that, given the geomorphology of the river system, the peak redshank count in the proposed development area represented almost 50% of the wintering population for the river. The presence of up to 4 greenshank was also of significance, given the low national, threshold index of 6–9 birds to register site importance for this species.

Available research based both on modelling and field studies (Sutherland, 1996; Burton et al., 2006) indicate that birds displaced as a result of habitat loss are most likely to suffer reduced fitness, increased mortality with a consequent reduction in regional populations due to competition for resources. This reinforces the commonly adopted precautionary principle that adjacent suitable habitats are similarly at carrying capacity and that displaced species cannot simply be absorbed elsewhere.

At the river ecosystem level, therefore, the development could, without adequate mitigation, result in a highly significant adverse impacts with implications for the local and possibly regional populations of bats and wading birds.

This was accordingly registered in the EIA and strategies for mitigation considered.

Box 2. Proposed Transit Development

A transit development has been proposed for an abandoned railway line. The environmental assessment for the scheme recorded some small patch localities of basic grassland with a few characteristic indicator species present such as upright brome (Bomus erectus), kidney vetch (Anthyllis vulneraria) and yellow wort (Blackstonia perfoliata). However, the vegetation community was, overall, dominated by coarse grasslands, tall herb and scrub comprising common to abundant plant species and the number of indicator species of diverse basic grasslands in any one area generally fell below the commonly adopted numerical criterion for the identification of grasslands of county value (5–6 indicator spp.).

However, a more detailed survey of the whole alignment, treating this as a linear ecosystem, recorded a total of 12 characteristic indicator species of basic grasslands, and the results suggested that ecological succession and the closure of scrub had punctuated a formerly diverse continuum of basic grasslands on the railway verges.

Given this ecological potential and the additional value of the former railway as a wildlife corridor and habitat mosaic, in particular its scrub formations, the site was assessed as of county value and a comprehensive mitigation package put into place involving retention and management of verge habitats where possible on the site, the creation of compensation basic grasslands off-site, equivalent in area to the total area of basic grasslands lost to the development, and a long-term management programme of enhancements to adjacent basic-grassland County Wildlife Sites, thereby enhancing ecological core areas and habitat networks at the local landscape scale.

Use of the corridor for animal movements (e.g. by badgers and foraging bats) also reinforced its valuation as a key linear system and mitigation was directed into preserving, as far as possible, this function.

Box 3. Greenfield Housing Development

A major housing development was proposed for a greenfield site in southern England, one of many such developments proposed in areas of arable and mixed farmland. While the site overall, being dominated by intensive arable farming, was of low habitat diversity, the bird community of arable farmland was typical with breeding species such as rook, barn owl, cuckoo, skylark, yellowhammer, reed bunting, tree sparrow, linnet and turtle dove with occasional wintering flocks of lapwing and golden plover, depending on the cropping regime of the arable land. Brown hare was also present, another typical species of the farmland landscape.

An ecosystem approach to evaluation in this context is problematic given the regional continuum of the agricultural landscape, although sub-elements such as the hedgerows, small watercourses and old field ponds can be addressed in terms of tree and shrub diversity and habitat structure, amphibian populations and the connective function of the hedgerows and field verges as part of the larger landscape ecological network. Master planning addressed the need to retain these features in a connected matrix of extensive public open spaces that linked to the wider countryside beyond; in particular, targeted at a great crested newt metapopulation. However, such on-site mitigation would not address the likely losses of the farmland bird and mammal community.

Bird surveys recorded a number of BAP species present as breeding populations. For some (e.g. song thrush, dunnock)—the development with the proposed mitigation strategy of extensive areas of open space being retained, encapsulating the key wildlife corridors—no significant impacts were anticipated. For other species, however (e.g. grey partridge, yellowhammer, turtle dove), it was concluded that the land-use change would probably result in the loss of the species from the site.

Developments in agricultural landscapes thus raise the issue of how to evaluate, for example, the significance of presence of one or possibly a number of BAP species dependent on farmland in the context of their highly probable loss from the area following development. At what level is it reasonable to require mitigation for the loss of low numbers of BAP species bearing in mind that a financial cost to ecological benefit ratio is relevant? An approach to this is considered below.

Table 4. Proposed indices for the assessment of farmland birds

Species	Status	Approximate UK population estimate	Updated NCC index	Population on site (breeding pairs)	Combined NCC/site-population index
Turtle Dove^a	BAP	44,000	3	2	6
Cuckoo^a	BAP	10,000–20,000	3	2	6
Barn owl	Schedule 1	4,000	4	1	4
Kestrel	BAP	36,800	3	1	3
Skylark	BAP	801,000–1,785,000	1.5	21	31.5
Linnet	BAP	556,000	2	4	8
Yellowhammer	BAP	792,000–1,200,000	1.5	18	27
Tree sparrow	BAP	68,000	3	1	3
Reed bunting^a	BAP	200,000	2	1	2
Combined Community Index					90.5
Note: ^aNCC community indexed.

Garland , L. and Markham , S . 2008 . Is important bat foraging and commuting habitat legally protected . Mammal News , Spring : 15 – 16 .

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